Laboratoire P.A.S.T.E.U.R.

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Intramolecularly Protein-Crosslinked DNA Gels: New Biohybrid Nanomaterials with Controllable Size and Catalytic Activity

Small 2017, 1700706

 

DNA micro- and nanogels—small-sized hydrogels made of a crosslinked DNA backbone—constitute new promising materials, but their functions have mainly been limited to those brought by DNA. Here a new way is described to prepare submicrometer-sized DNA gels of controllable crosslinking density that are able to embed novel functions, such as an enzymatic activity. It consists of using proteins, instead of traditional base-pairing assembly or covalent approaches, to form crosslinks inside individual DNA molecules, resulting in structures referred to as intramolecularly protein-crosslinked DNA gels (IPDGs). It is first shown that the addition of streptavidin to biotinylated T4DNA results in the successful formation of thermally stable IPDGs with a controllable crosslinking density, forming structures ranging from elongated to raspberry-shaped and pearl-necklace-like morphologies. Using reversible DNA condensation strategies, this paper shows that the gels can be reversibly actuated at a low crosslinking density, or further stabilized when they are highly crosslinked. Finally, by using streptavidin–protein conjugates, IPDGs with various enzymes are successfully functionalized. It is demonstrated that the enzymes keep their catalytic activity upon their incorporation into the gels, opening perspectives ranging from biotechnologies (e.g., enzyme manipulation) to nanomedicine (e.g., vectorization).

Redesigning the QA binding site of Photosystem II allows reduction of exogenous quinones

Nat. Commun., 8, 15274

 

Strategies to harness photosynthesis from living organisms to generate electrical power have long been considered, yet efficiency remains low. Here, we aimed to reroute photosynthetic electron flow in photosynthetic organisms without compromising their phototrophic properties. We show that 2,6-dimethyl-p-benzoquinone (DMBQ) can be used as an electron mediator to assess the efficiency of mutations designed to engineer a novel electron donation pathway downstream of the primary electron acceptor QA of Photosystem (PS) II in the green alga Chlamydomonas reinhardtii. Through the use of structural prediction studies and a screen of site-directed PSII mutants we show that modifying the environment of the QA site increases the reduction rate of DMBQ. Truncating the C-terminus of the PsbT subunit protruding in the stroma provides evidence that shortening the distance between QA and DMBQ leads to sustained electron transfer to DMBQ, as confirmed by chronoamperometry, consistent with a bypass of the natural QA°- to QB pathway.

Photoinduced Chromophore Hydration in the Fluorescent Protein Dreiklang Is Triggered by Ultrafast Excited-State Proton Transfer Coupled to a Low-Frequency Vibration

J. Phys. Chem. Lett. 2017, 8, 1489−1495

 

Because of growing applications in advanced fluorescence imaging, the mechanisms and dynamics of photoinduced reactions in reversibly photoswitchable fluorescent proteins are currently attracting much interest. We report the fi rst timeresolved study of the photoswitching of Dreiklang, so far the only fluorescent protein to undergo reversible photoinduced chromophore hydration. Using broadband femtosecond transient absorption spectroscopy, we show that the reaction is triggered by an ultrafast deprotonation of the chromophore phenol group in the excited state in 100 fs. This primary step is accompanied by coherent oscillations that we assign to its coupling with a low-frequency mode, possibly a deformation of the chromophore hydrogen bond network. A ground-state intermediate is formed in the picosecond− nanosecond regime that we tentatively assign to the deprotonated water adduct. We suggest that proton ejection from the phenol group leads to a charge transfer from the phenol to the imidazolinone ring, which triggers imidazolinone protonation by nearby Glu222 and catalyzes the addition of the water molecule.

 

 

 

Selective Electrochemical Bleaching of the Outer Leaflet of Fluorescently Labeled Giant Liposomes

Chem. Eur. J., 23,1–8, 2017

 

Electrochemistry and confocal fluorescence microscopy were successfully combined to selectively bleach and monitor the fluorescence of NBD (7-nitrobenz-2-oxa-1,3- diazole)-labeled phospholipids of giant liposomes. Three types of giant unilamellar vesicles have been investigated, the fluorescent phospholipids being localized either mainly on their outer-, inner-, or both inner/outer leaflets. We established that only the fluorescent lipids incorporated in the outer leaflet of the vesicles underwent electrochemical bleaching upon reduction. The relative fluorescence intensity decay was quantified all along the electrochemical extinction through an original fluorescence loss in electrobleaching (FLIE) assay. As expected, the reorganization of the fluorescent phospholipids followed diffusion-driven dynamics. This was also evidenced by comparison with fluorescence loss in photobleaching (FLIP) and the corresponding numerical model. The value of the lateral diffusion coefficient of phospholipids was found to be similar to that obtained by other methods reported in the literature. This versatile and selective bleaching procedure appears reliable to explore important biological and pharmacological issues.

 

L'eau, une histoire trouble - Podcast France Culture

L’eau est un des éléments qui nous est le plus familier, mais recèle encore bien des mystères. Comment se sont construites les théories physiques et chimiques sur l’eau ? Quelles sont nos connaissances actuelles sur cette substance ?